Upgrading of crude naphthalene crystals by hot detergent washing



May 18, 1954 c. B. OGlLVlE UPGRADING OF CRUDE NAPHTHALENE CRYSTALS BYHOT DETERGENT WASHING Filed Nov. 1, 1951 INVENTOR CLINTON B. OG/ZV/[ATTO R N EY Patented May 18, 1954 UPGRADING 0F. CRUDE NAPHTHALENECRYSTALS BY HOT DETERGENT WASH- ING Clinton B. Ogilvie, Martinsville, N.J., assignor to American Cyanamid Company, New York, N. Y., acorporation of Maine Application November 1, 1951, Serial No. 254,260

3 Claims.

This invention relates to an improvement in the purification ofnaphthalene, and more particularly, to an improvement in the separationof oily impurities from naphthalene of coal tar or petroleum origin.

The impurities associated with crude naphthalene will vary, dependingupon whether the naphthalene was obtained as a by-product from coal taror petroleum. It is common practice to combine naphthalene from bothsources in storage and crude stocks will vary both in naphthalenecontent and in the impurities present. Our invention is applicable tothe purification of naphthalene from either petroleum or coal tarsources and is particularly effective in the upgrading of naphthaleneprimarily derived from coal tar.

In the refining of naphthalene from coal tar sources, it is customary toremove the tar acids by suitable washing treatments with strong alkali.Naphthalene from petroleum sources does not have any considerableportion of tar acids, and therefore with such naphthalenes the Washingtreatment is usually omitted. The naphthalene, free from tar acids, isthen generally placed in the so-called crystallizing pans or boxes whereit is permitted to stand for a long period of time, a matter of weeks oreven months, until a considerable portion of the oily materials drainout. The partially purified naphthalene is then hot pressed or sometimescentrifuged to remove further amounts of oily materials, followed bysulfuric acid washing and fractional distillation. It is thus possibleto obtain naphthalene of a high purity, as evidenced by its meltingpoint of about 79.7 (3;, which represents a. purity of at least 98.5%.Naphthalene of this purity is normally required when it is to be usedfor dyestuff intermediates, for example, in the preparation ofnaphthols. Naphthalene melting at 78 C. is satisfactoryfor thepreparation of phthalic anhydride.

The ordinary refining of naphthalene presents a serious problem from thestandpoint of equipment capacity, particularly in the crystallizing pansor boxes, where the time of residence of the naphthalene is excessivelylong. The other steps such as hot pressing, sulfuric acid washing, andfractional distillation, also add to thecost of the refined naphthaleneand require extensive equipment.

Various processes have been proposed for removing oily impurities fromnaphthalene and the separation of similar organic solids. In oneprocess, naphthalene was crystallized in relatively large flat crystalsand washed with brine. This process, while effecting some purification,was not sufiicient to replace any considerable number of the timeandequipment-consuming steps. The production of large crystals requiredvery slow cooling and little or no agitation. While with shallow depthsit is theoretically possible to cool for less than an hour, in general,the cooling extends over a number of hours, for example, six to nine.With a typical crude coal tar naphthalene, the crystals may be broughtup to a setting point of a little over 74 C. This process, therefore,did not solve the problem of producing sufiiciently cheap naphthalene ofphthalic anhydride intermediate grade.

Gould, in his Patent No. 1A81,197,- has described an efficient method ofprecipitating naphthalene in crystalline form by heating the crudenaphthalene above the melting point and pouring it into cold water withagitation. The crystals when separated, however,- still occlude a largeamount of the oily impurities and the napthalene must be purifiedfurther before it can be used.

According to the present invention, we have.

found that naphthalene in the crystalline form as obtained by Gouldsprocess or some similar process, may be upgraded by hot detergentwashing to produce a product melting at 73 C. or better, in a singlestep. It is an advantage of the present invention that when this newprocess improved method to'be described in conjunction with the drawingwhich is a diagrammatic fl'o'wsheet of my new'process.

In the drawing, l' is a tank containing the wash solution and surroundedby a heating jacket which'controls the temperature of the wash solution.

A feed pump 2 supplies the spray nozzles with the wash solution underpressure.

The washing rate is determined by means'of a flow m'eter3 and thewhizzer type centrifuge 4" has'an outlet at'the bottom to permitrecovery of. the used wash solution.

acvaocs In upgrading naphthalene according to my invention, I chargecrude naphthalene crystals melting at about 68 C. or above into thecentrifuge 4 at low speed. I then prepare the wash solution of desiredcomposition and heat it in tank I. The centrifuge is rotated at highspeed while the wash solution is forced by pump 2 through flow meter 3to the spray nozzles within the centrifuge. After the specified volumeof wash water has been applied to the crude naphthalene crystals, Iwring the cake in the centrifuge for a short while. The centrifuge isthen stopped and the upgraded material removed from the basket.

In order to obtain naphthalene melting at 78 C. or better, from thecrude crystals melting at 68 C. or above, it is necessary to controlcertain steps in my process which are critical. The temperature of theWash solution is particularly important because too low a temperaturewill result in a product below specification. For this reason, thetemperature of the wash solution should be above 65 C. and in general, Iheat the wash solution to 75 C. There is considerable cooling due to therapid motion of the centrifuge basket and to the low temperature of thecrude naphthalene crystals at the start of the washing operation. Thus,the first wash water which enters the centrifuge at 75 C. leaves thecentrifuge at 53 C. and toward the end of the washing process thetemperature of the effluent has increased to 74. The final temperatureof the combined wash water is 59 C. For this reason, the wash solutionmay be heated to temperatures considerably above the setting point of ithe crude naphthalene crystals and the upper limit of the temperaturerange would be that temperature which would result in fusion of thecrude naphthalene crystals charged into the centrifuge.

The detergent used is also critical because some detergents do notproduce a naphthalene of satisfactory melting point and others introducefoaming and caking. We have discovered that surface active agents whichdo not produce insoluble calcium salts are satisfactory in that theywill produce specification grade naphthalene.

Anionic surface active agents that are derived from high molecularWeight organic sulfonates have certain operating advantages over thecationic and nonionic type. One such advantage is the lack of foamingwhich is particularly important with centrifuges of the size used inlarge commercial operations. Another advantage is the elimination ofcaking. Certain cationic and nonionic surface active agents although notprecipitated by calcium ions, will permit the build-up of a cake on theinside jacket of the centrifuge and between the basket and thecentrifuge screen. This necessitates the shutdown of equipment and theperiodic cleaning of the centrifuge which naturally increases thewashing cost. We particularly prefer to use di(2-ethyl hexyl) sodiumsulfosuccinate in the wash water because that particular reagent keepsthe centrifuge and basket clean at all times, thus enabling theoperation to be used on a continuous basis without shutdown. The amountof surface active agent may be varied, but we have found approximatelybased on the total wash solution, was satisfactory. An increase in thisamount did not give any appreciable improvement in results, butdecreasing the amount gave results approaching a straight water washwhich was unsatisfactory.

The amount of wash solution is related to' its temperature, but ingeneral, approximately five parts wash water at 75 C. is used for onepart crude naphthalene crystals. If less wash water is used, thetemperature must be raised to obtain comparable results. Increasing theamount of wash water slows up the process and introduces new problems,so that we have found the ratio of approximately five to one to be aneffective compromise.

In addition to the surface active agents, it is advantageous to addone-half of one percent sodium carbonate to the wash solution. Sodiumcarbonate primarily reduces the water occluded by the centrifugedcrystals, and secondarily, has a beneficial effect on the setting pointof the purified crystals. More than one-half of one percent sodiumcarbonate, however, has the opposite effect on occluded moisture andcannot be used without introducing foaming problems.

,Sodium carbonate also aids in breaking the emul- Crude naphthalene,predominantly of coal tar origin, having a setting point of 69.9 C. andcontaining 78.8% naphthalene, was charged into a centrifuge and washedat high speed (1450 R. P. M.) with 133 parts of wash solution containing0.125% of aerosol OT (di(2-ethyl hexyl) sodium sulfosuccinate) at atemperature of 35 C. The wash solution was sprayed on the cake at a rateof about 25 parts per minute. The charge was wrung at high speed untilessentially free of wash solution and the centrifuge then stopped. Thecake when removed from the basket was approximately 92.8% pure and had asetting point of 76.83 C. This product did not meet specificationbecause the temperature of the wash solution was too low. The yield ofnaphthalene recovered was better than 90% based on the naphthalenepresent in the centrifuge charge. The moisture content of the cake was24.8%.

Emample 2 The procedure of Example 1 was followed, but the temperatureof the wash solution was increased to 60 C. The naphthalene was upgradedfrom 692 C. setting point (77.6% purity) to 77.8" C. (94.8% purity),again indicating that the temperature of the wash solution was too low.The yield was approximately 88%. The final moisture content of the cakewas 19.3%.

Example 3 The procedure of Example 1 was followed, using a wash solutionat a temperature of 70 C. Upgrading from 690 C. S. P. (77.25% purity) to78.50 C. S. P. (96.2% purity) was achieved with an 80% yield on thebasis of naphthalene charged. Final moisture content of the cake was12.8%.

Example 4 The procedure of Example 1 was followed using the washsolution at a temperature of 80 C. Upgrading from 703 C. S. P. (79.5%purity) to 79.35 C. S. P. (97.9% purity) was achieved with about 70.0%yield. Final moisture content of the cake was 6.1%.

Example 5 To the wash solution of Example 3, 0.5% soda ash was added andthe procedure was repeated according to that example. Upgrading from68.5 C. S. P. (76.3% purity) to 785 C. S. P. (96.2% purity) was achievedwith better than 80% yield on the basis of real naphthalene charged.Final moisture content of the cake was 5.4%.

Example 6 Example 7 The procedure of Example 3 was followed with 0.125%by-weight of NI-l-182 (product of one mole of dimerized fatty acid andtwo moles of Carbo Wax #4000) being used in place of aerosol OT in thewash solution. Upgrading from 69.1 C. S. P. (77.4% purity) to 78.10 C.S. P. (95.4% purity) was achieved with an 88.6% yield on the basis ofreal naphthalene charged. Final moisture content of the cake was 8.2%.Considerable caking was noted in the centrifuge basket.

Example 8 The procedure of Example 3 was repeated, using the Washsolution at a temperature of 65 C. The naphthalene crystals wereupgraded from 69.6 1 C. to 780 C.

Example 9 The procedure of Example 8 was repeated, but the aerosol OT(di(2-ethy1 hexyl) sodium sulfosuccinate) was replaced by an equalweight of soap. The crude naphthalene crystals were upgraded from asetting point of 68.78 C. to a setting point of 77.41 C.

Example 10 The procedure of Example 8 was repeated, but the aerosol OT(di(2-ethyl hexyl) sodium sulfosuccinate) present in the wash solutionwas omitted. The naphthalene crystals were upgraded from a setting pointof 69.30 C. to a final setting point of 77.23 C. by washing with wateralone.

Example 11 The procedure of Example 3 was repeated, but the aerosol OT(di(2-ethyl hexyl) sodium sulfosuccinate) present in the wash solutionwas replaced by an equal weight of mixed amylnaphthalene sodiumsulfonate. The naphthalene crystals were upgraded from a setting pointof 693 C. to a setting point of 78.15 C.

It will be recognized that the effluent from the centrifuge may bereheated and recycled, thus improving the overall yield of my process.In addition, the oily layer which separates from the effluent emulsionmay be recycled to the crude naphthalene stock and reprecipitated incrystalline form.

I claim:

1. A process for upgrading crude naphthalene crystals which compriseswashing said crystals in a centrifuge with a wash solution containingless than 1% di(2-ethyl hexyl) sodium sulfosuccinate, the temperature ofsaid solution being above C., but insuificient to melt said naphthalenecrystals.

2. A process for upgrading crude naphthalene crystals which compriseswashing said crystals in a centrifuge with a wash solution containingless than 1% di 2-ethyl hexyl) sodium sulfosuccinate, and approximatelyone-half of one percent sodium carbonate, the temperature of saidsolution being above 65 C., but insufiicient to melt said naphthalenecrystals.

3. A process for upgrading crude naphthalene crystals which comprisesWashing said crystals in a centrifuge with a wash solution containingless than 1% di(2-ethyl hexyl) sodium sulfosuccinate, the amount of saidwash solution being approximately 5 times the amount of the crudenaphthalene crystals, and the temperature of said solution being above65 C., but insufiicient to melt the naphthalene crystals.

References Cited in the file *of this patent UNITED STATES PATENTSNumber Name Date 1,441,417 Gould Jan. 9, 1923 2,078,963 Miller May 4,1937 2,403,127 Schulze July 2, 1946 2,499,236 Van Gilder et al. Feb. 28,1950 FOREIGN PATENTS Number Country Date 611,213 Great Britain Oct. 27,1948

1. A PROCESS FOR UPGRADING CRUDE NAPHTHALENE CYRSTALS WHICH COMPRISESWASHING SAID CRYSTALS IN A CENTRIFUGE WITH A WASH SOLUTION CONTAININGLESS THAN 1% DI(2-ETHYL HEXYL) SODIUM SULFOSUCCINATE, THE TEMPERATURE OFSAID SOLUTION BEING ABOVE 65* C., BUT INSUFFICIENT TO MELT SAIDNAPHTHALENE CRYSTALS.